The present invention relates to sealing devices adjacent a gas flowpath of a gas turbine engine and, more particularly, to a ring seal having a seal dam on a high pressure side of the ring seal adjacent an outside diameter thereof.
Current gas turbine engine technology uses labyrinth seals to isolate gas flowpaths, reduce circulations, minimize parasitic losses, and maintain cavity pressures to control rotor thrust balance. These seals control the leakage of high pressure gas by throttling it through a series of annular restrictions formed radially between a set of labyrinth "teeth" and rub strips. The teeth and rub strips are pre-machined to provide a fixed radial clearance at engine assembly level. The rub strips are abradable to allow the teeth to rub lightly during dynamic operation thus providing a minimum of clearance.
Wear on the knife edge of the labyrinth teeth and wear on the corresponding rub strip severely limits the ability of labyrinth seals to maintain a small clearance. Some wear is caused by high radial and centrifugal thermal expansions and contractions. In addition, wear results from axial translations and gyroscopic excursions that occur over a range of operating shaft speeds. Wear rate is generally a function of air temperatures, pressure and, in the case of aircraft engines, high G-maneuvers and hard landings.
As a result of this inability to maintain a small clearance, the majority of labyrinth seals leak excessively. The excessive leakage of labyrinth seals located at primary and secondary flowpaths has a detrimental effect on engine efficiency, performance, fuel consumption, and/or turbine blade life.
Thus, a need is seen for a seal mechanism which maintains a small clearance level and is generally impervious to wear caused by the operating conditions of an engine.